Apparatus for simultaneous determination of carbon-temperature in liquid steel during blowing

ABSTRACT

IN A SAMPLING VESSEL FOR RECEIVING LIQUID STEEL DURING BLOWING, INDEPENDENT THERMOCOUPLES ARE MOUNTED ON THE INSIDE OF THE BOTTOM OF SAID VESSEL AND PURGING AIR IS EJECTED THROUGH THE SIDE APERTURE OF SAID VESSEL THROUGH AN AUXILIARY LANCE SUPPORTING SAID VESSLE. A PERMEABLE STOPPER IS PROVIDED AT THE TOP OF THE VESSEL WHICH PERMITS FREE FLOW OF SAID PURGIN AIR BUT PREVENTS COUNTER FLOW OF LIQUID STEEL IN SAID VESSEL.

March 23, 1971 NORIYOSHI NAGAOKA ETAL 3,572,124

- APPARATUS FOR SIMULTANEOUS DETERMINATION OF CARBON-TEMPERATURE IN LIQUID STEEL DURING BLOWING Filed April 14, 1969 4 Sheets-Sheet 1 FIGI (PRIOR ART) FIG 2 (PRIOR ART) March 23, 1971 NORIYOSHI NAGAOKA ET AL 3,572,124

APPARATUS FOR SIMULTANEOUS DETERMINATION OF CARBON-TEMPERATURE IN LIQUID STEEL DURING BLOWING Filed April 14, 1969 r 4 Sheets-Sheet 2 FIG 5 2. 'I Q a 2 M '8 I 51" I E i 46 I I Q ki l} i l 12i 1;, i 5

March 23, 1971 Filed April 14, 1969 v NORIYOSHI NAGAOKA ETAL APPARATUS FOR SIMULTANEOUS DETERMINATION OF CARBON-T IN LIQUID STEEL DURING BLOWING 4 Sheets-Sheet s EMPERATURE FIG 7 Temperature F March 23, 1971 NORIYOSHI NAGAOKA ETAL 3,572,124

APPARATUS FOR SIMULTANEOUS DETERMINATION OF CARBON-TEMPERATURE IN LIQUID STEEL DURING BLOWING Filed April 14, 1969 v 4 Sheets-Sheet 4 Tlme (sec) Y I: 5 (LS i /M 4 XS 6 fig Temperature F) United States Patent US. Cl. 73-341 4 Claims ABSTRACT OF THE DISCLOSURE In a sampling vessel for receiving liquid steel during blowing, independent thermocouples are mounted on the inside of the bottom of said vessel and purging air is ejected through the side aperture of said vessel through an auxiliary lance supporting said vessel. A permeable stopper is provided at the top of the vessel which permits free flow of said purging air but prevents counter flow of liquid steel in said vessel.

BACKGROUND OF THE INVENTION This invention relates to an apparatus for measuring simultaneously and in a short period of time both the carbon content and bath temperature of the molten steel in furnaces during blowing, whereby to etfect dynamic control of the blowing thus improving the quality and productivity of steel ingot.

Various methods have been proposed to obtain the above mentioned data. One method involves dropping a sampling vessel 1 into the molten steel through a throat into the furnace, causing the molten steel to enter the vessel, immediately raising the vessel and measuring the bath temperature by means of a thermocouple therein, as shown in FIGS. 1 through 4.

The carbon content in molten steel bath is determined by measuring the temperature of a liquidus line during the course of temperature variation in the sampling vessel 1 and then effecting heat analysis. In order to obtain the correct value of the temperature of the liquidus line, the measuring of the bath temperature is made by an expendable immersion thermocouple which is lowered by means of a special device. The time required for measuring both of the temperatures is about 15 seconds, after dropping the sampling vessel in the bath.

Generally, however, various measurements in furnaces during blowing are diflicult because the blowing state is varied at a high speed so that the following problems will arise:

(1) Where the sampling vessel is dropped into the molten steel bath, the slags having different temperatures over the molten steel bath often enter the vessel, thus impairing accurate measurement of the liquidus temperature.

(2) During measurement of the liquidus line temperature, a shrinkage hole is developed from the upper part to the lower part of the cup in the central part of the sample piece, thus impairing accurate measurement.

(3) As the subject to be measured comprises a small quantity of the steel piece contained in the withdrawn sampling vessel, the falling rate of the temperature thereof is faster than that of the bath in the furnace so that the result of the measurement is not stable.

(4) As the lead-in wire connected to a measuring instrument has a two circuit structure as shown in FIG. 4, it is subject to melting or short circuiting from exposure to the combustion flame in the furnace, and to the hot "ice slag layer and molten steel. Thus, it is impossible to provide a measurement compensation. Further, in order to repeatedly use said wire, considerable time delays are required. Thus, the operating eliiciency of the drop-in thermocouple is very low.

SUMMARY OF THE INVENTION It is therefore an object of this invention to provide a novel detector for measuring simultaneously the bath temperature and the liquidus line temperature.

Another object of this invention is to provide a novel sampling vessel which prevents molten steel from running into said vessel until the vessel is immersed in the molten steel bath.

Still another object of this invention is to provide an improved sampling vessel having means to permit free flow of gas while preventing counter-flow of molten steel.

Briefly stated, in accordance with this invention there is provided an apparatus for simultaneous determination of carbon content and temperature of molten steel bath during blowing comprising a sampling vessel having an aperture through its side wall, a first thermocouple in the botom of said vessel, 2. second thermocouple on the outside of the bottom of said vessel, an auxiliary lance to support said sampling vessel, means to eject gas through said aperture via said auxiliary lance and a stopper made of porous materials provided at the upper portion of said sampling vessel which permits free flow of said gas but which presents counterflow of molten steel.

BRIEF DESCRIPTION OF THE DRAWINGS In accompanying drawings:

FIG. 1 shows a schematic view of a prior art apparatus for measuring carbon content and temperature in molten steel;

FIG. 2 is a sectional view taken along a line XX in FIG. 1;

FIG. 3 is a longitudinal sectional view of a detector taken along a line Y--Y in FIG. 1;

FIG. 4 shows a cross-sectional view taken along a line Z-Z in FIG. 1;

FIG. 5 shows a longitudinal sectional view of a vessel embodying this invention;

FIG. 6 shows a manner of utilizing the vessel for BOF;

FIG. 7 is a graph showing a typical liquidus line temperature and;

FIG. 8 is a curve to show the variation in the temperature of the molten steel bath.

DESCRIPTION OF THE PREFERRED EMBODIMENT As shown in FIGS. 5 and 6, the measuring apparatus of this invention comprises a temperature detector 1 and an auxiliary lance 2. The detector 1 includes vessel 10 defining a sampling chamber 4 having a side aperture 3 through which molten steel flows into the vessel, and including a thermocouple 5 for measuring the temperature of the liquidus line positioned at the bottom of the sampling chamber 4. To thermally and mechanical- 1y protect the sampling vessel 10, the vessel 10 is covered with a paper sleeve 6 and an additional thermocouple 7 is provided to project beyond the bottom surface of the said sampling vessel 10 to measure the bath temperature.

With this apparatus, the molten steel running into the sampling chamber 4 from the side aperture 3 is deoxidized by means of a deoxidizer '8 which is Al-wire or the like. Then, the liquidus line of the molten steel in the vessel is detected by means of the thermocouple 5 at the bottom of said vessel so that the carbon content of the molten steel is determined by said liquidus line. As the sampling vessel is lowered into the molten steel bath, the paper sleeve 6 which is a cardboard or the like, burns to evolve gas when it comes to contact with the molten steel thus causing vigorous agitation of the molten steel nearby. Accordingly, measurement of the gas temperature and liquidus line is rendered very unstable by thermocouples and 7. To prevent this, the wall of said aperture and the outside of said vessel bottom are covered with shields 9 of metal or other refractory material to stabilize thermocouples 5 and 7. During the blowing of slag, a layer having a temperature different from that of the molten steel covers the molten steel. Consequently, when said vessel is immersed into the bath, the slag may enter into said vessel and hinder accurate measurement of the bath tempera ture. To obviate this difficulty, a suitable gas such as air is ejected outwardly through said aperture 3 from the inlet port 11 provided at the upper end of said vessel 10, such an air-purge being carried out through an inner tube of the auxiliary lance 2 connected to the above detector 1.

As diagrammatically shown in FIG. 6, during blowing or immediately after blowing in the BOP process, the novel apparatus is lowered into the bath with air being purged through lance 2. The apparatus passes through the slag layer and then reaches a desired depth of the bath. When the above air-purging is stopped, at this point liquid steel without slag is permitted to run into the chamber 4 of the sampling vessel 10. A suitable stopper 17 is provided at the upper portion of the inlet 11 to prevent the molten steel in said vessel from counter-flowing toward the auxiliary lance. Moreover, the stopper 17 can protect a connector 15 and the compensating lead wires 16, which are connected to auxiliary lance 2 by a proper steel tube via connection 18, from being damaged. The stopper 17 is made of a porous refractory material or of a permeable material to provide free flow of said purging air, while preventing counter-flow of said liquid steel up into lance 2.

When the novel apparatus reaches a predetermined depth in bath, the temperature thereof is detected by thermocouple 7 on the outside of said vessel, which is covered with a steel cap. The temperature is displayed by an external thermometer 13 via the lead wires 16 extending through auxiliary lance 2. The manner in which the bath temperature varies as the measuring apparatus goes down and then goes up is shown by the curve of FIG. 8. The apparatus indicates the temperature of the slag layer while it is lowered through the slag layer and then indicates the bath temperature as it is lowered past the slag layer. When the apparatus is drawn up, it will again indicate the temperature of the slag layer.

When the sampling vessel is drawn up immediately after being immersed in the bath, the temperature of liquid steel in said vessel is indicated by a precision thermometer 14 via compensating lead wires extending through the auxiliary lance, thus providing a curve as shown in FIG. 7. At an equilibrium temperature of 2779 F., the falling rate of the liquidus line temperature due to the presence of such impurities as Si, Mn, P and S in steel is presumed and is corrected by said rate and then the carbon content in steel is easily determined.

The measuring apparatus of the present invention is provided with two thermocouples, one for measuring the liquidus temperature and the other for measuring the temperature of the molten steel bath whereby it is possible to simultaneously detect the carbon content and the temperature of the molten steel with high accuracy and in an extraordinarily short period of time of less than 10 seconds. As a result, it is not necessary to tilt the furnace for measuring the temperature and for analyzing the composition of the steel. When using this measuring apparatus during blowing, predetermination of temperature, blowing pattern and such will help stabilize the refining operation, improve accuracy of detecting the constituents, thereby improving productivity. Further, as it is possible to measure not only the temperature of molten steel but also the temperature and thickness of the slag layer, it is now possible to observe the details of the blowing operation.

Since the detector 1 is removably connected to auxiliary lance 2 by a steel tube having screw threads on both ends, it is possible to exchange the detecting member 1 in a very short time, for example, within 5 seconds. Further air purging effectively prevents the slag layer, which has a different temperature from the molten steel, from running into the sampling vessel when the detector is immersed into the molten steel bath. The permeable stopper 17 permits free flow of purging air but prevents counter flow of molten steel and hence the damage caused thereby.

Finally, the measuring apparatus of this invention can also be used for open-hearth furnaces and for electric furnaces in the same manner as conventional consumption type thermocouple thermometers to measure the temperature and carbon content of steel.

While the invention has been shown and described in terms of a preferred embodiment, many changes and modifications may occur to one skilled in the art without departing from the true spirit and scope of the invention as defined in the appended claims.

What is claimed is:

1. Apparatus for simultaneous determination of carbon tent and temperature of molten steel during blowing comprising a sampling vessel having an aperture through its side wall;

a first thermocouple on the inside bottom of said sampling vessel;

a second thermocouple on the outside of the bottom of said sampling vessel;

an auxiliary lance supporting said sampling vessel; and

means to purge said sampling vessel including:

means for passing air through said auxiliary lance to said vessel and through said aperture; and

a permeable stopper provided at upper portion of said sampling vessel and below said auxiliary lance, said stopper permitting free passage of said air to said vessel but preventing counterflow of molten steel from said vessel to said auxiliary lance.

2. The measuring apparatus according to claim 1 wherein said first and second thermocouples are independent and are connected to independent indicators with compensating lead wires extending through said auxiliary lance.

3. The measuring apparatus according to claim 1 wherein said sampling vessel is provided with a paper sleeve and is covered with metal or other refractory material at least near the wall of said side aperture.

4. The measuring apparatus according to claim 1 wherein the second thermocouple is covered with a metal cap.

References Cited UNITED STATES PATENTS 3,255,634 6/1966 Cavalier 73425.6 3,298,069 1/1967 Acre 7342.1 3,321,973 5/1967 Anderson 73359 3,357,250 12/1967 Lowdermilk 73425.4 3,367,189 2/1968 Curry 73425.4 3,455,164 7/1969 Boyle 73354 3,463,005 8/1969 Hance 73-425.4

OTHER REFERENCES American Institute of Mining and Metallurgical Engineers, volume 122, 1936, p. 197.

S. CLEMENT SWISHER, Primary Examiner D. E. CORR, Assistant Examiner US. Cl. X.R. 

